1. Field of the Invention
The present invention is generally directed to an electric fan and, more particularly, to a rotor or impeller assembly for an electric fan. More specifically, the present invention is directed to a unique arrangement and technique for securing one or more fan blades to a hub utilized on an electric fan.
2. Description of the Related Art
Impellers having a number of metallic fan blades attached to a hub, also commonly referred to as rotor assemblies or propellers, are widely used in a variety of domestic, commercial, and industrial fan equipment. For instance, impellers are typically used in HVAC equipment, ventilation equipment, and a wide variety of air circulation fans. In many commercial or industrial environments, such as in an automobile plant, impellers are found in great quantity in air circulation fans located above numerous, individual work stations.
Impellers designed for use in industrial and commercial environments must be capable of withstanding long durations of use, and therefore must be highly durable. Additionally, the efficiency of an impeller is highly important, particularly when used in an industrial environment where hundreds or possibly thousands of units may be installed. A typical measure of impeller performance is the amount of air output by the impeller, conventionally measured in cubic feet per minute (CFM), but important factors such as overall power consumption and the heat rise of the device employing the impeller (e.g., a fan) are also monitored when evaluating impeller, or fan, performance. As used herein, the term "fan" means any device or equipment utilizing an impeller, including, although not necessarily limited to, an electric fan, an air circulator, HVAC equipment and ventilation equipment.
In view of the importance of impeller performance, manufacturers of fans or impeller components are constantly attempting to improve their performance. The conventional approach to improving the performance of a fan or impeller used on a fan has been to alter the shape of the fan blade used on the impeller. In this regard, many past attempts have been made to improve fan performance by modifying the shape of the fan blade, often resulting in complex parabolic or hyperbolic blade configurations.
A primary problem with the prior art approach of modifying the shape of the fan blade to achieve better fan performance is the expense associated with the design, testing, and tooling required to arrive at the desired blade configuration. Additionally, in many circumstances, it is difficult or impractical to use preferred durable materials, such as metal, to achieve the configuration desired.
Efforts to improve fan performance have also included varying the pitch at which the blades of a fan attack the surrounding air. Increasing the pitch of the blade increases drag, and hence increases air flow. However, increasing the pitch of the blades increases the strain on the motor, and there are thus practical limits to which the pitch can be increased.
Accordingly, the need exists for a fan having improved performance, and namely an electric fan with increased air flow characteristics, decreased power requirements, and which causes less heat rise in the motor associated with the fan. Additionally, the need exists for an electric fan, and particularly an impeller for an electric fan, which is simple and inexpensive to manufacture, and does not require redesigning the blade or developing expensive tooling for a new blade configuration. In this regard, their is a need for an improved fan which uses existing impeller components, such as a conventional hub and blades.
In short, the need exits for a cost effective solution to increasing fan performance without the significant investment required for reconfiguring and tooling a new fan blade. The present invention fulfills these and other needs, and overcomes the drawbacks of the prior art.